We know that the change in kinetic energy is going to be equal to the size of the change in potential energy. That's the way we start off a lot of questions in this section. So we have one half 'mv' initial squared, is 'mgh'. This is the change in kinetic energy, because the final kinetic energy is 0, since the slid stops. We'll solve for 'v', multiplying both sides by 2; and noticing that the 'm' is a common factor that cancels. Taking the square root of both sides also, 'v' is square root of 2'gh'. Which is the square root of 2 times 9.8 meters per second squared, times 1.35 meters and this gives # meters per second, must have been the initial speed.